Background: Application of laser energy onto exposed dentinal tubules provides instantaneous relief from dentin hypersensitivity. The aim of the present study was to compare between CO 2 and Nd:YAG laser irradiation for their sealing ability on human dentinal tubules when treated with and without fluoride varnish, using Scanning Electron Microscopy. Materials and Methods: Twenty extracted human intact third molar teeth were selected. A total of six samples were obtained from each tooth. One hundred and twenty dentin samples from 20 teeth were then divided into six groups with 20 samples in each group. These slabs were treated with 17% ethylenediaminetetraacetic acid (EDTA) for 5 min and with 5% NaOCl for the next 2 min for removal of the smear layer. Each of the samples from a single tooth was then subjected to six different treatment protocols according to the groups given below.
Group 1 (n = 20) : CO 2 laser
Group 2 (n = 20) : Nd:YAG laser
Group 3 (n = 20) : Varnished with fluoride and lased with CO 2 laser
Group 4 (n = 20) : Varnished with fluoride and lased with Nd:YAG laser
Group 5 (n = 20) : Varnished with fluoride
Group 6 (n = 20) (control) : Not subjected to lasing and fluoride application
All samples were examined under scanning electron microscope. Results were subjected to statistical analysis using one-way analysis of variance (ANOVA) and the multiple comparisons among groups were carried out by Student's t-test. Results: Compared to conventional fluoridation or laser irradiation, in the treatment of dentin hypersensitivity, CO 2 lasers in combination with fluoride varnish appear to show better efficacy than either treatment modality alone.